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CURRENT LOAD LEVELING IN AN AC CYCLE-STEALING CONTROL APPLICATION

IP.com Disclosure Number: IPCOM000130153D
Publication Date: 2005-Oct-13
Document File: 3 page(s) / 11K

Publishing Venue

The IP.com Prior Art Database

Abstract

Current solid freeform fabrication machines produced by 3D Systems, Inc. use an expensive transformer which is manually configured depending on where the machine is to be delivered to accommodate for the different electric power standards around the world (U.S., Asian, or European). The present invention utilizes digital technology to eliminate the need for the transformer by providing the ability to shut off the load to balance the load to a desired power used by the machine. Although this invention provides a significant cost and operating advantage, this appears to be a fairly common way to adapt power equipment to operate in various power supply standards.

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CURRENT LOAD LEVELING IN AN AC

CYCLE-STEALING CONTROL APPLICATION

            This technical disclosure relates to all solid freeform fabrication machines which consume power that may be delivered according to

U.S.

, Asian, or European standards.

SUMMARY OF THE INVENTION

            Current solid freeform fabrication machines produced by 3D Systems, Inc. use an expensive transformer which is manually configured depending on where the machine is to be delivered to accommodate for the different electric power standards around the world (

U.S.

, Asian, or European).  The present invention utilizes digital technology to eliminate the need for the transformer by providing the ability to shut off the load to balance the load to a desired power used by the machine.

            Although this invention provides a significant cost and operating advantage, this appears to be a fairly common way to adapt power equipment to operate in various power supply standards.

PURPOSE OF THE INVENTION

            Cycle-stealing is an acknowledged scheme in which whole cycles or portions of cycles of a voltage or current AC-signal are “stolen,” i.e., shut off at some load, so that the actual time-average voltage or current experienced at the load is proportionately lower than if the whole signal was to be applied to the load.

            One side effect of utilizing this scheme is an imbalance in the input current or voltage waveform as the cycles are switched on and off across the load.

            This invention describes a means to balance this loading across multiple channels of cycle-stolen control lines.  It is especially advantageous in maintaining a steady-state AC line current when AC line voltage is “cycle-stolen” on multiple switched heater channels, for example, as in the case of the InVision™ Si2 product.

PRIOR ART

            Cycle stealing, as a method to remove whole cycles or portions of cycles of an AC signal, is a well-known and old method of controlling AC signals, especially across AC heater loads.

            Suppose multiple parallel loads are switched on/off simultaneously, as in when a cycle-stolen output waveform is applied to many parallel loads.  Also suppose that this cycle stolen output waveform applied to many parallel loads is derived from a single input waveform.  When the cycles are “stolen,” i.e. switched off, then the applied voltage at the load and therefore the current required at the input is minimized.  Conversely, when the cycles are not “stolen,” the current is maximized.  There can be a large variation in input current as the control system applied this cycle-stolen waveform across large parallel loads.  This can be problematic for appliances or machines that are plugged into ganged AC power outlets.  The fluctuation in current can cause other appliances and machines in the same supply line to exp...